Device certificate based appliance configuration

ABSTRACT

Embodiments of the present invention address deficiencies of the art in respect to configuring a computing appliance and provide a method, system and computer program product for device certificate based virtual appliance configuration. In one embodiment of the invention, a virtual appliance secure configuration method can be provided. The method can include mounting non-volatile storage to the virtual appliance, retrieving a device certificate from the mounted storage and extracting a signature from the device certificate, activating the virtual appliance in a network domain and acquiring an adapter address and unique identifier for the virtual appliance, and authenticating the signature with the adapter address and unique identifier to ensure a unique active instance of the virtual appliance.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.11/848,557, filed Aug. 31, 2007, now allowed, and is also a Continuationof U.S. application Ser. No. 11/848,573, filed Aug. 31, 2007, nowallowed, which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of configuring a computingdevice for deployment into a computing environment and more particularlyto securely configuring a virtual appliance in a computing environment.

2. Description of the Related Art

Computing devices range from the simplistic to the complex, from thesmallest form factor to room-consuming behemoths. Despite the greatdisparity in nature of computing devices, all share a commoncharacteristic—the need for configuration. Simplistic computing devicescan be enabled prior to delivery to the customer through factory levelconfiguration, while larger systems often require configuration by thecustomer on site, or by an on site expert installing the computingsystem. For many devices, configuration is not a one time event, but anongoing process as device upgrades are applied throughout the productlifecycle of a computing device.

The simplest of computing devices oftentimes involve only a single fixedstorage unit like a hard disk drive, a processor, dynamic memory andexternal low volume storage such as a memory key or floppy disk drive.To configure the computing device, then, requires little more thanmanual application of configuration data at boot time, often through abasic input output system (BIOS) interface. It is also well known toapply firmware and flash configuration of a computing device throughfirmware configuration applications distributed along with theconfiguration data itself. Equally as well known, the networkcommunications interface of a computing device can be used as a conduitthrough which a configuration can be applied to a computing device.

Configuring a single computing device can be a relatively simple andstraightforward affair, however, managing the wide-scale configurationof many hundreds if not thousands of computing devices can be morechallenging. To effectuate such an extensive configuration, oftentimesinformation technologists perform the configuration in a pilot instanceof a computing environment within a virtualized host. Once the efficacyand stability of the configuration can be verified in the virtualizedhost, it is of little consequence to move the virtualized host in fileform to the target computing device for activation as a configuration ofthe target computing device.

Of note, the use of a virtualized host to implement a configuration canbe especially helpful in configuring a computing appliance. A computingappliance is known in the art as a self-contained information technology(IT) system that can be plugged into an existing IT infrastructure tocarry out a single purpose, making it comparable to a consumer appliancesuch as the toaster. Computing appliances have gained a foothold inenterprise IT systems because of their simplicity, reliability, ease ofuse and lower cost compared with general purpose computers. Theappliance is designed to address a specific IT operation from within aclosed architecture that may contain an operating environment, storageand specific applications. The purpose of an appliance can be to provideadditional processing power, network storage or monitoring, oranti-virus and security.

Though the computing appliance can be implemented as a single purposestand alone computing platform, a virtual form of the computingappliance has evolved to provide an even greater degree of flexibility.In this regard, a virtual appliance is a computing appliance deployedwithin a virtual environment hosted by a computing platform. To the enduser, there is little if any functional distinction between a computingappliance and a virtual appliance, however, from a deploymentperspective, distributing a virtual appliance to the end user can beorders of magnitude more simple to manage—especially in configuring andupdating the virtual appliance.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention address deficiencies of the art inrespect to configuring a computing appliance and provide a novel andnon-obvious method, system and computer program product for devicecertificate based virtual appliance configuration. In one embodiment ofthe invention, a virtual appliance secure configuration method can beprovided. The method can include mounting non-volatile storage to thevirtual appliance, retrieving an encrypted device certificate from themounted storage, verifying the device certificate signature, activatingthe virtual appliance in a network domain using constraints in thedevice certificate to ensure a unique active instance of the virtualappliance.

In one aspect of the embodiment, mounting a virtualized storage deviceon the virtual appliance such as an image of a storage device selectedfrom the group consisting of a floppy drive, a rewritable compact disc(CDRW), a rewritable digital video disc (DVDRW), a universal serial bus(USB) key, or any of a number of varieties of flash memory cards/sticks.In another aspect of the embodiment, mounting a secure storage device tothe virtual appliance such as a real or virtualized security chipset. Ineither circumstance, in yet another aspect of the embodiment, retrievinga device certificate from the key ring using symmetrical decryptionwhere the key ring is located on the mounted storage.

Notably, the method additionally can include extracting a signedextension from the device certificate, identifying one or moreconfiguration parameters, and configuring the virtual applianceaccording to the configuration parameters. Also, the method additionallycan include periodically verifying the logic performing theauthenticating of the signature and of the adapter address to ensure aunique active instance of the virtual appliance.

In another embodiment of the invention, a virtual appliance dataprocessing system can be provided. The system can include a virtualenvironment and a virtual appliance executing within the virtualenvironment. The system also can include device certification validationlogic. The logic can include program code enabled to retrieve anencrypted device certificate from mounted storage and to verify thesignature from the device certificate, to activate the virtual appliancein a network domain using constraints from the certificate and ensure aunique active instance of the virtual appliance.

The mounted storage might be an image of a storage device selected fromthe group consisting of a floppy drive, CDRW, DVDRW, a universal serialbus (USB) key, or any of a number of varieties of flash memorycards/sticks. Alternatively, the mounted storage might be a securestorage device such as a real or virtualized security chipset. In eithercase, the layer 2 network adapter address known as the media accesscontrol (MAC) address and a password are used to form a key which isused to decrypt the keyring held on the mounted device so that thedevice certificate can be recovered. In addition, the system can includesigned extensions disposed in the device certificate, the extensionsdefining configuration parameter(s) for the virtual appliance whichmight include layer 3 network address constraints. Finally, as yetanother option, the system can include integrity verification logicincluding program code enabled to verify the device certificationvalidation logic.

Additional aspects of the invention will be set forth in part in thedescription which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The aspectsof the invention will be realized and attained by means of the elementsand combinations particularly pointed out in the appended claims. It isto be understood that both the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute partof this specification, illustrate embodiments of the invention andtogether with the description, serve to explain the principles of theinvention. The embodiments illustrated herein are presently preferred,it being understood, however, that the invention is not limited to theprecise arrangements and instrumentalities shown, wherein:

FIG. 1 is a pictorial illustration of a process for device certificatebased virtual appliance configuration;

FIG. 2 is a schematic illustration of a virtual appliance enabled fordevice certificate based configuration;

FIG. 3 is a flow chart illustrating a process for generating a key ringenclosing a device certificate for device certificate based virtualappliance configuration; and,

FIG. 4 is a flow chart illustrating a process for configuring a virtualappliance with the key ring of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention provide a method, system andcomputer program product for device certificate based virtual applianceconfiguration. In accordance with an embodiment of the presentinvention, a device certificate can be established for a virtualappliance. The device certificate can include a signature created by acertificate authority such as the appliance manufacturer, a public keyfor the virtual appliance, and a formal name that can include, by way ofexample, a layer two (2) virtual network adapter address for the virtualappliance in combination with a layer three (3) network address or namefor the virtual appliance. One or more extensions can also be includedin the certificate, for example configuration limitations to be appliedto a configured instance of the virtual appliance. Finally, the devicecertificate can be placed in a key ring along with the private key forthe public key in the device certificate and the key ring issymmetrically encrypted using a different hash of a customer suppliedpassword/pin and the virtual appliance layer 2 network adapter address.

The key ring can be distributed on portable media for use in configuringone or more instances of the virtual appliance. In this regard, acustomer can use the key ring to configure any number of instances ofthe virtual appliance, though only a single active instance can bepermitted due to the requirement of a unique layer 2 network address onan active network segment and constraints on the allowed layer 3 networkaddress contained in the certificate extensions.

Specifically, device certificate validation logic can decrypt the keyring in the intended target device using a customer supplied passwordand the layer 2 network adapter address, for instance a MAC address, ofthe running virtual appliance. As the layer 2 network address must beunique within a LAN segment this has the side effect of assuring onlyone instance of a virtual device is active on a segment. Moreover,configuration limitations within the device certificate can be appliedto the virtual appliance to yet further manage and control thecapabilities of the virtual appliance including constraints on the layer3 addresses and names used by the appliance.

In illustration, FIG. 1 pictorially depicts a process for devicecertificate based virtual appliance configuration. As shown in FIG. 1, avirtual appliance 110 can be deployed by a customer 130 utilizing aconfiguration provided by the manufacturer 120. Specifically, themanufacturer 120 can issue a device certificate 140 containingconstraints on both the configuration and operation of the appliance andplace this certificate with its corresponding public key SK in a keyring 160 protected by a key 150 formed by hashing the hash 180 of thecustomer 130 provided password and a MAC address which must be used bythe network adapter of the running appliance 110. The encrypted key ringis then transmitted to the customer who makes it available to theappliance 110 as a virtual device 190

The virtual appliance 110 can extract the MAC (layer 2) address fromit's network adapter and can retrieve a password from the customer 130.Thereafter, the virtual appliance 110 can hash the MAC addressconcatenated with a hash of the password 180 to reconstruct thesymmetric key 150 which allows the key ring to be unlocked giving accessto the device certificate and its corresponding symmetric key. Thevirtual appliance 110 then can verify the signature in the devicecertificate and can use the certificate name and extensions for variousconfiguration functions including constraining either or both of thelayer 3 network address and the name of the virtual appliance 110.

A device certificate 140 can be signed by the certificate authority ofthe manufacturer and can be verified by comparing the hash of the signedfields (such as extensions, name, device public key) with the signaturevalue decrypted by the public key 180 of the certificate authority thatresides on the appliance hard drive 170 along with this verificationcode. Note that the customer 130 password hash 180A optionally can beplaced on the hard drive 170 of the virtual appliance 110.

Inherent to the access of the device certificate 140 is the requirementthat a unique adapter layer 2 address subsist for the virtual appliance110. As such, the utilization of the device certificate 140 ensures onlya single active instance of the virtual appliance 110 on the LAN segmentby the customer 130. Additionally, configuration limitations on the useof the virtual appliance 110 can be applied through the devicecertificate 140 as specified within the device certificate 140 in theform of extensions or by naming. One such limitation may be in the layer3 network addresses or names allowed hence further restricting the useof the appliance within the network of the customer.

In more particular illustration, FIG. 2 schematically depicts a virtualappliance data processing system enabled for device certificate basedconfiguration. The system can include a host computing device 210 andcorresponding writable storage 220 supporting the operation of a virtualenvironment 230. The virtual environment 230 can execute within aseparate operating system, or the virtual environment 230, itself can bethe operating system supported by the host computing device 210. Avirtual appliance 240 can be disposed within the virtual environment 230and can access the physical network interface provided for the hostcomputing device 210 through virtual environment 230 as a virtualadapter layer 2 address and a virtual layer 3 network address.

Device certification validation logic 250 can be coupled to the virtualappliance 240. The device certification validation logic 250 can includeprogram code enabled to configure the virtual appliance 240 at the timeof initialization and to ensure the unique instance of the virtualappliance 240 as a form of licensure control. In this regard, devicesecurity memory 200, for instance a virtual or real floppy disk orsecurity chipset, can include a key ring 290. The key ring 290 caninclude a device certificate 280A one or more device certificateextensions 280B disposed within the device certificate 280A, and aprivate key 280C for the virtual appliance 240. Optionally, additionalcertificates (not shown) can be included in the key ring 290 for use byother applications such as connecting with a lightweight directoryaccess protocol (LDAP) server for directory services or a Web server forserving secure content.

The key ring 290 further can be encrypted with a symmetric key which isthe hash of the virtual appliance 240 adapter MAC address concatenatedwith the hash 270 of a password originally provided by the customer. Acopy of the password hash 270 can be stored in writable storage 220 tofacilitate automatic activation of the appliance without requiring humaninteraction. In operation, the program code of the device certificatevalidation logic 250 uses the public key of the manufactures certificateauthority to verify the device certificates signature which assures allof the other fields of the certificate have not been modified since itwas issued.

Notably, the device certificate 280A once validated containsrestrictions that are applied to the initialization of the networkstack. In one aspect of the embodiment, the network address can includea combination of “host.domain_name” and IP address for the virtualappliance 240. In a second aspect of the embodiment, however, thedynamic assignment of an IP address to the virtual appliance 240 throughthe dynamic host control protocol (DHCP) can be accommodated by omittingthe IP address and the usual checks are performed periodically duringexecution to make sure that those address have not been modified in thedomain name server (DNS) and that the DNS has not been spoofed.

As a further measure of protection, integrity verification logic 260 canbe coupled to the virtual appliance 240. The integrity verificationlogic 260 can include program code enabled to verify the integrity ofthe device certification validation logic 250. For instance, the programcode of the integrity verification logic 260 can be enabled to compare ahash of the device certification validation logic 250 to a known hash.Alternatively, the program code of the integrity verification logic 260might employ a scheme such as that used by the open source CommonSecurity Services Manager of the Common Data Security Architecture(CDSA) in order to ensure that the device certification validation logic250 has not been modified or otherwise compromised.

Integral to the operation of the virtual appliance data processingsystem of FIG. 2, a key ring can be generated for a specificdistribution of a virtual appliance to a specific customer and providedto the customer as a file either in the form of an image of removablemedia or as a parameter to the virtual driver representing a securitychip set for the virtual appliance. In illustration, FIG. 3 is a flowchart depicting a process for generating a key ring enclosing a devicecertificate and private device key for the virtual applianceconfiguration. Beginning in block 300, one or more virtual applianceconfiguration parameters or rules can be defined for the virtualappliance and encapsulated within corresponding device extensions.

In block 310 MAC address (layer 2) is created for the virtual appliancenetwork adapter from the block of addresses assigned to the manufacturerusing a process similar to the way a manufacturer of real network cardswould assign a MAC to each card on the production line. In block 320 aprivate/public key pair is generated. In block 330 the layer 3 networkconstraints are set using interaction with the customer to set valuesappropriate for the network segment where the appliance will bedeployed. At a minimum this means choosing a host name and domain namefor the appliance instant. In block 340 extensions for variousconfiguration parameters are created to represent the licensed use ofthe appliance instance.

In block 350, a digital signature can be generated using the private keyof the manufacturer to encrypt the hash over the other portions of thecertificate, and in block 360, signed device certificate can be placedinto a key ring along with the private key for the virtual appliance andother trusted root certificates including the manufacturers certificate.In block 370, a password can be retrieved from the customer intended toreceive the virtual appliance. Thereafter, in block 380, the key ringcan be symmetrically encrypted using a hash of the virtual appliancenetwork adapter MAC address concatenated with a hash of the password.Finally, in block 390 the encrypted key ring and the MAC address can bereturned to the customer in an appropriate form.

The key ring produced according to the process of FIG. 3 can be utilizedat the time of initialization for the virtual appliance. In particular,the content of the key ring—specifically the device certificate—can beused to ensure not only a single active instance of the virtualappliance, but also to configure the single active instance of thevirtual appliance according to the configuration parameters reflectedwithin the extensions in the device certificate. In more particularillustration, FIG. 4 is a flow chart illustrating a process forconfiguring a virtual appliance with the key ring of FIG. 3. Beginningin block 410, the virtual appliance can be initialized for use in anetwork domain. In block 420, external storage such as a virtual floppydisk, virtual security chipset can be mounted for access by the virtualappliance.

In block 430, an adapter address for the virtual appliance networkadapter can be retrieved. Of note, the customer must configure thevirtual environment with the MAC address assigned by the manufacturer.In block 440, the end user can be prompted for a password which ishashed and saved in the appliance storage for automated access on futureinitializations. Thereafter, in block 450 the key ring can be selectedand decrypted using a symmetric encryption key produced as a hash of theMAC concatenated with the password hash. Once the key ring has beendecrypted, the device certificate can be retrieved from the key ring inblock 460 and in block 470 the certificate can be verified by hashingits non-signature fields and comparing that with the signature fielddecrypted using the manufactures public key taken from the manufacturercertificate also found on the key chain. Again, of note, themanufacturer certificate can be validated and ultimately a public rootkey or root certificate which is part of the appliance code can bereferenced to complete the process of generating trust in the devicecertificate. At this point other checks can be preformed such aschecking the certificate is being used within its valid date range andfor the purpose issued.

In block 480, the layer 3 network restrictions can be retrieved from thecertificate and the layer 3 network can be activated within theseconstraints. If there where any problems up to this point as determinedin decision block 490 then an error message can be generated in block520 and the appliance can stop operating. Otherwise, in block 500 thenon-network virtual appliance configuration can be retrieved from thedevice certificate extensions and in block 510, the virtual applianceconfiguration parameters can be applied to the virtual applianceinstance being initialized.

Embodiments of the invention can take the form of an entirely hardwareembodiment, an entirely software embodiment or an embodiment containingboth hardware and software elements. In a preferred embodiment, theinvention is implemented in software, which includes but is not limitedto firmware, resident software, microcode, and the like. Furthermore,the invention can take the form of a computer program product accessiblefrom a computer-usable or computer-readable medium providing programcode for use by or in connection with a computer or any instructionexecution system.

For the purposes of this description, a computer-usable or computerreadable medium can be any apparatus that can contain, store,communicate, propagate, or transport the program for use by or inconnection with the instruction execution system, apparatus, or device.The medium can be an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system (or apparatus or device) or apropagation medium. Examples of a computer-readable medium include asemiconductor or solid state memory, magnetic tape, a removable computerdiskette, a random access memory (RAM), a read-only memory (ROM), arigid magnetic disk and an optical disk. Current examples of opticaldisks include compact disk-read only memory (CD-ROM), compactdisk-read/write (CD-R/W) and DVD.

A data processing system suitable for storing and/or executing programcode will include at least one processor coupled directly or indirectlyto memory elements through a system bus. The memory elements can includelocal memory employed during actual execution of the program code, bulkstorage, and cache memories which provide temporary storage of at leastsome program code in order to reduce the number of times code must beretrieved from bulk storage during execution. Input/output or I/Odevices (including but not limited to keyboards, displays, pointingdevices, etc.) can be coupled to the system either directly or throughintervening I/O controllers. Network adapters may also be coupled to thesystem to enable the data processing system to become coupled to otherdata processing systems or remote printers or storage devices throughintervening private or public networks. Modems, cable modem and Ethernetcards are just a few of the currently available types of networkadapters.

1. (canceled)
 2. A virtual appliance secure configuration methodcomprising: mounting a virtualized non-volatile storage device on thevirtual appliance; retrieving an encrypted device certificate from themounted virtualized non-volatile storage device and extracting asignature from the encrypted device certificate; verifying the encrypteddevice certificate by hashing non-signature fields of the devicecertificate and comparing the hashed non-signature fields of the devicecertificate with a signature field decrypted using a manufacturer publickey; and, activating the virtual appliance in a network domain andacquiring an adapter address and unique identifier for the virtualappliance.
 3. The method of claim 2, wherein the virtualizednon-volatile storage device on the virtual appliance is selected fromthe group consisting of a floppy drive, a rewritable compact disc, arewritable digital video disc, and a universal serial bus (USB) key. 4.The method of claim 2, wherein the virtualized non-volatile storagedevice on the virtual appliance comprises static memory in associationwith a security chipset for the virtual appliance.
 5. The method ofclaim 2, wherein retrieving the encrypted device certificate from themounted storage comprises: loading a key ring from the virtualizednon-volatile mounted storage device, the key ring including theencrypted device certificate for the virtual appliance, one or moreextensions specifying configuration limitation for an instance of thevirtual appliance disposed with the device certificate, and also aprivate key for the virtual appliance; symmetrically decrypting the keyring; and, retrieving the encrypted device certificate from thesymmetrically decrypted key ring.
 6. The method of claim 2, wherein theunique identifier for the virtual appliance is an Internet protocol (IP)address for the virtual appliance.
 7. The method of claim 5, furthercomprising: extracting the one or more an extensions from the encrypteddevice certificate; identifying a configuration parameter in the one ormore extensions; and, configuring the virtual appliance according to theconfiguration parameter.
 8. (canceled)
 9. A computer program productcomprising a non-transitory computer usable medium embodying computerusable program code for virtual appliance secure configuration, thecomputer program product comprising: computer usable program code formounting a virtualized non-volatile storage device on the virtualappliance; computer usable program code for retrieving an encrypteddevice certificate from the mounted virtualized non-volatile storagedevice and extracting a signature from the encrypted device certificate;computer usable program code for verifying the encrypted devicecertificate by hashing non-signature fields of the device certificateand comparing the hashed non-signature fields of the device certificatewith a signature field decrypted using a manufacturer public key; and,computer usable program code for activating the virtual appliance in anetwork domain and acquiring an adapter address and unique identifierfor the virtual appliance.
 10. The computer program product of claim 9,wherein the virtualized non-volatile storage device on the virtualappliance is selected from the group consisting of a floppy drive, arewritable compact disc, a rewritable digital video disc, and auniversal serial bus (USB) key.
 11. The computer program product ofclaim 9, wherein the virtualized non-volatile storage device on thevirtual appliance comprises static memory in association with a securitychipset for the virtual appliance.
 12. The computer program product ofclaim 9, wherein the computer usable program code for retrieving theencrypted device certificate from the mounted virtualized non-volatilestorage device comprises: computer usable program code for loading a keyring from the mounted virtualized non-volatile storage device, the keyring including the encrypted device certificate for the virtualappliance, one or more extensions specifying configuration limitationfor an instance of the virtual appliance disposed with the devicecertificate, and also a private key for the virtual appliance; computerusable program code for symmetrically decrypting the key ring; and,computer usable program code for retrieving the encrypted devicecertificate from the symmetrically decrypted key ring.
 13. The computerprogram product of claim 9, wherein the unique identifier for thevirtual appliance is an Internet protocol (IP) address for the virtualappliance.
 14. The computer program product of claim 12, furthercomprising: computer usable program code for extracting one or moreextensions from the encrypted device certificate; computer usableprogram code for identifying a configuration parameter in the one ormore extensions; and, computer usable program code for configuring thevirtual appliance according to the configuration parameter. 15.(canceled)
 16. A virtual appliance data processing system comprising: avirtual environment; a virtual appliance executing within the virtualenvironment; and device certification validation logic comprisingprogram code enabled to retrieve a device certificate from mountedstorage and extract a signature from the device certificate, verify thedevice certificate by hashing non-signature fields of the devicecertificate and comparing the hashed non-signature fields of the devicecertificate with a signature field decrypted using a manufacturer publickey, activate the virtual appliance in a network domain, and acquire anadapter address and unique identifier for the virtual appliance.
 17. Thesystem of claim 16, wherein the mounted storage is storage selected fromthe group consisting of a floppy drive and a universal serial bus (USB)key.
 18. The system of claim 16, wherein the adapter address is a mediaaccess control (MAC) address and the network address is a combination ofhost.domain name and Internet protocol (IP) address.
 19. The system ofclaim 16, further comprising a key ring containing the devicecertificate for the virtual appliance, one or more extensions specifyingconfiguration limitations for an instance of the virtual appliancedisposed with the device certificate, and also a private key for thevirtual appliance.
 20. The system of claim 16, wherein the devicecertification validation logic further comprises program code enabled toextract one or more extensions specifying configuration limitations foran instance of the virtual appliance disposed in the device certificate,identify at least one configuration parameter in the one more extensionsfor the virtual appliance, and configure the virtual appliance accordingto the at least one configuration parameter.
 21. The method of claim 2,wherein the encrypted device certificate includes the signature createdby a certificate authority, a public key for the virtual appliance, aformal name for the virtual appliance, and one or more extensionsspecifying configuration limitations for an instance of the virtualappliance.
 22. The method of claim 21, wherein the formal name for thevirtual appliance includes a layer two virtual network adapter addressfor the virtual appliance in combination with one of a layer threenetwork address and a name for the virtual appliance.
 23. The system ofclaim, wherein the device certificate includes the signature created bya certificate authority, a public key for the virtual appliance, aformal name for the virtual appliance, and the one or more extensionsspecifying configuration limitations for an instance of the virtualappliance.